There are known many differing types of apparatus for separating various products including agricultural products from spurious material, i.e. including for example, clods, stones and vegetation.
Conventional airflow separation devices use an air stream directed toward a mixture of products and other material. The lighter products of the mixture are propelled the furthest. Thus generally such devices propel the lighter material upwardly while the heavy products go downwardly. This type of air separator is not suitable for processing a high rate of feed material containing a large percentage of clods.
A particularly efficient type of device commonly known as a "stoner" is basically an uphill vibrating conveyor with a porous surface. When carefully controlled air passes through the porous surface lighter particles are lifted from the conveyor surface and are moved downward by the force of gravity. The heavier particles remain in contact with the vibrating surface and move upward.
Devices of the stoner type are conventionally employed in fixed locations such as in packing or processing plants. They are not suitable for use in the field for on-line processing of harvested goods for a number of reasons.
The "stoner" device is extremely sensitive to the angle of inclination of the porous surface. A slight change in angle has a large effect on the vibrational forces required to drive the products up the slope. For example, if the grid is tilted toward one side, even slightly, the vibrational movement of the surface which effectively lowers the coefficient of friction causes a large percentage of the material to "pile up" on the low side and interfere with the effective operation of the device. Also if the slope of the surface increases slightly the flow of the products up the surface is curtailed. Since the ground surface under field conditions is relatively uneven, the precision maintenance of the slope angle is rendered exceedingly difficult if not impracticable. Thus leveling means can be employed, more power can be used but both alternatives are costly and/or time consuming.
A further difficulty with employing devices of the "stoner" type under field conditions is that the airflow generated under the operating field conditions contains a very large amount of vegetation debris which tends to be forced up against the underside of the grid by the airflow and thus blocks the air passage through the grid. This problem is not encountered in processing plants where the surrounding atmosphere is relatively clean and free of spurious material or alternatively an air supply is provided from a location remote from the operational area.
Also, the fact that devices of the "stoner" type employ vibrating elements makes it preferable that the devices be firmly anchored in a fixed location or costly and complicated counter-balancing equipment is employed. Thus the present "stoners" are unsuitable for incorporation into moving or movable support structures and field use.
The present invention seeks to overcome the deficiencies of prior art apparatus and to provide separation apparatus suitable for use under actual field conditions for on-line separation of agricultural products as they are harvested.